1. Technical Field of the Invention
This invention is related to oil well production equipment and more particularly to tubing anchors in oil well production tubing strings.
2. State of the Prior Art
Typical oils wells have well casings comprising lengths of larger diameter pipes set and cemented into well bore holes extending downwardly from the surface of the ground into or through one or more subterranean, oil-bearing, geological formations called reservoirs. Conventional completions in such wells include perforating the casing with holes at depths in one or more of the reservoirs that allow the crude oil and other fluids in the reservoir or reservoirs to flow into the well casing. Some wells have enough natural pressure in the reservoir to force the crude oil and other fluids all the way through the well casing to the surface of the ground, where the crude oil can be collected and transported away from the well for further refinement and use. Other wells do not have enough natural reservoir pressure to force the crude oil all the way to the surface of the ground, so pumps have to be used to lift the crude oil in the casing out of the well. Raising and collecting the crude oil from the well is commonly known as producing the well, and equipment used in that process is commonly called production equipment. There are many different kinds of production pumps used in oil wells for pumping crude oil in well casings to the surface of the ground, one of the oldest and yet most common popular of which is the reciprocating piston-type pump, sometimes also called sucker rod pump, stroking pump, traveling piston pump, or barrel pump.
Reciprocating piston-type pumps typically have a down-hole pump assembly comprising a hollow cylinder barrel mounted on the down-hole end of a string of production tubing that extends downwardly from a hanger on the well surface, through the well casing, and into the crude oil in the well casing. A piston containing a traveling, one-way check valve is positioned the cylinder barrel in a slidable manner that allows the piston and the traveling one-way check valve to move reciprocally upwardly and downwardly in the cylinder barrel, and a standing, one-way check valve is mounted on the bottom of the cylinder barrel. A sucker rod extends downwardly from a polish rod near the surface of the ground, through the production tubing string, and into the cylinder barrel where it is attached to the piston. The polish rod extends slidably through a stuffing box to connect the sucker rod to a pump jack or other pump driver for repetitively pulling the sucker rod upwardly and letting it down to reciprocate the piston in the cylinder barrel upwardly and downwardly. The stuffing box creates a seal around the polish rod to seal the interior of the tubing from the exterior of the well. The standing one-way check valve allows fluid in the casing to flow into the cylinder barrel as the piston is pulled upwardly by the pump jack and sucker rod, and the traveling one-way check valve allows that fluid in the cylinder barrel to flow through the piston as the piston moves downwardly in the cylinder barrel. Continuous reciprocal motion of the piston in combination with the one-way flow of fluid through the standing and traveling check valves results in the fluid in the well being pumped from the casing upwardly through the production tubing string to the surface of the well.
As explained in U.S. Pat. Nos. 5,139,090 and 5,327,975 issued to J. Land, both of which are incorporated herein for all that they disclose, in wells equipped with reciprocating piston-type pumps, rotating the production tubing string with respect to the sucker rod in the tubing string while concurrently placing the production tubing string in tension reduces severity of wear in areas where the sucker rod tends to rub against the inside surface of the tubing string and overall increases the useful life of the tubing string. Both of the aforesaid U.S. Pat. Nos. 5,139,090 and 5,327,975 describe apparatus and methods for anchoring the tubing string at or near the bottom of the well adjacent to the cylinder barrel in a rotatable manner to accommodate such tensioning and rotation of the production tubing string. The tubing anchor catcher with rotatable mandrel is described in the U.S. Pat. No. 5,327,975 as an improvement over the tubing rotator with down hole swivel described in U.S. Pat. No. 5,139,090. However, it has been found that tubing anchor catchers with rotatable mandrels made as described in the U.S. Pat. No. 5,327,975 are not reliably easy to set and are even more difficult to release and retrieve from the well, which results in problems when the tubing string, down hole pump components, and other production equipment in the well have to be removed from the well. Too often, inability to release those tubing anchor catchers quickly and easily is frustrating and time-consuming, sometimes causing the operator to resort to the back-up system of pulling hard on the tubing string to shear the shear pins in the anchor to release the slips that anchor the device in the well casing. Unfortunately, however, some tubing strings are in severely worn or in weakened condition, and such extraordinary tension breaks and severs the tubing string before the shear pins of the anchor shear, thereby causing the operator have to perform extraordinary recovery procedures, including, for example, drilling and fishing the remaining tubing and the tubing anchor catcher out of the well. Such extraordinary procedures not only add to the recovery time and costs but also destroy the tubing anchor catchers so that they cannot be used again.
The foregoing examples of related art and limitations related therewith are intended to be illustrative, but not exclusive or exhaustive, of the subject matter. Other aspects and limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings.